1. Field of the Invention
The present invention relates to a homogenizer for use, for example, when mechanically mixing and agitating a plurality of mutually incompatible liquids to atomize, emulsify, and disperse the liquids. Particularly, the present invention relates to an improvement for obtaining a sharp grain diameter distribution in conformity with a target grain diameter when atomizing the liquids.
2. Description of the Related Art
In recent years, NOx and suspended particulate matter (SPM) such as soot, which are contained in exhaust gas of a diesel engine, have been a great social problem from a viewpoint of an environment load. As measures for solving such a problem relating to the exhaust gas, a diesel engine using water emulsion fuel has been proposed and brought to a commercial stage. This water emulsion fuel is fuel prepared by mixing and emulsifying light oil and water, and it has been reported that amounts of SPM and NOx emissions are significantly lowered in the diesel engine using the fuel.
This water emulsion fuel is, for example, one prepared in such a manner that oil and water are mixed at a ratio of 1:1, followed by atomization of the mixed matter to a grain diameter of approximately 1 μm, and emulsification thereof. In order to ensure stable engine combustion, it is important for a grain diameter distribution to concentrate on a narrow range centered on 1 μm without being expanded to a great extent.
Conventionally, as an apparatus for mixing and agitating two mutually incompatible liquids like water and oil, various types of homogenizers are publicly known, which are frequently used in production equipment for foods, chemical products, or the like, experimental plants, etc. Among these homogenizers, a so-called rotor/stator type homogenizer, a high-pressure homogenizer, and the like are known as homogenizers suitable for producing emulsions.
As the rotor/stator type homogenizer, one whose brand name is “Megatron (http://www.kinematica.ch/English/)”, which is made by KINEMATICA AG (Switzerland), one whose brand name is “Clearmix (http:www.organo.co.jp/prod/clearmix/)”, which is made by ORGANO CORPORATION, and the like, are known. Each of these rotor/stator type homogenizers includes a cylindrical stator fixed inside an agitation chamber, and a rotor which is accommodated in a hollow of the stator and imparted with a predetermined number of revolutions by a motor, the stator and rotor having a plurality of radially formed flow passages. After being mixed, the two mutually incompatible liquids are supplied to a hollow of the rotor by a pump. When the rotor starts to rotate in a state where these liquids are being supplied, a centrifugal force is applied to the liquids, which are then ejected from the radial flow passages formed in the rotor to enter a clearance between the rotor and the stator, further entering radial flow passages of the stator. The stator does not rotate but remains stationary, so that when the rotor starts to rotate, a vortex flow is generated in the liquids existing in the radial flow passages of the rotor and the stator. Furthermore, a shearing force in accordance with a rotational speed of the rotor is applied to the liquids having entered the clearance between the rotor and the stator. By means of energy of the vortex flow and shearing force, the two liquids are homogenized and eventually discharged as an emulsion to the outside through the radial flow passages formed in the stator.
In order to homogenize more efficiently, in other words, atomize the two liquids in this rotor/stator type homogenizer, it is important to apply a great shearing force to the liquids introduced into the clearance between the rotor and the stator. For this purpose, it is important to set the clearance defined between the inner peripheral surface of the stator and the outer peripheral surface of the rotor to be small. However, in practice, the clearance between the stator and the rotor cannot be set very small, and thus the rotor/stator type homogenizer is not suitable for producing an extremely fine grained emulsion of which grain diameter is no more than 1 μm. Meanwhile, in the case of throwing extremely large energy to the homogenizer by increasing the number of revolutions of the rotor or in other ways, though a production of the emulsion with the fine grain diameter can be expected, the produced emulsion has disadvantages in that the grain diameter distribution thereof does not exhibit sharp characteristics and that the grain diameter of the emulsion is undesirably distributed in a wide range.
Meanwhile, as the latter- high-pressure homogenizer, for example, one whose brand name is “Nanomizer,” which is made by Nanomizer Corporation, is known. This high-pressure homogenizer includes a generator in which capillaries having a hole diameter of approximately 0.25 mm are formed, and a high-pressure pump which fills, with pressure, the capillaries of the generator with a liquid. The high-pressure homogenizer is constructed in such a manner that two liquids to be made into an emulsion are mixed together and then are passed through the capillaries of the generator, whereby energy of a shock wave and cavitation is applied to the liquids in the capillaries, and an emulsion with a fine grain diameter is obtained due to the energy. This high-pressure homogenizer has an advantage in that an emulsion with a smaller grain diameter can be obtained in comparison with the rotor/stator type homogenizer described above because an amount of the energy thrown to the liquids per unit area is large. However, the high-pressure homogenizer has a problem in that there is an upper limit (approximately 500 cps) to the viscosity of the liquids to be atomized, and that types of liquids which can be processed by the high-pressure homogenizer are limited. Moreover, the high-pressure homogenizer has a problem in that an amount of the liquids, which can be processed per unit time, is extremely small because the liquids are passed through the capillaries with an extremely small inner diameter, and that, in order to increase a throughput, it is necessary to raise pressure generated by the above-described high-pressure pump, leading to undesirable enlargement of pump equipment in scale. Furthermore, though the high-pressure homogenizer can produce the emulsion with the fine grain diameter of approximately 1 μm, a grain diameter distribution of the produced emulsion has a width of approximately 0.5 μm with the fine grain diameter of 1 μm as the center. Thus, it cannot be said that the grain diameter distribution exhibits sharp characteristics.